enforce loading=lazy att to rendered images html

backend/app/store/formatter.go

@@ -59,6 +59,7 @@ func (f *CommentFormatter) FormatText(txt string) (res string) {
 		res = conv.Convert(res)
 	}
 	res = f.shortenAutoLinks(res, shortURLLen)
+	res = f.lazyImage(res)
 	return res
 }
 
@@ -108,3 +109,19 @@ func (f *CommentFormatter) unEscape(txt string) (res string) {
 	}
 	return res
 }
+
+// lazyImage adds loading=“lazy” attribute to all images
+func (f *CommentFormatter) lazyImage(commentHTML string) (resHTML string) {
+	doc, err := goquery.NewDocumentFromReader(strings.NewReader(commentHTML))
+	if err != nil {
+		return commentHTML
+	}
+	doc.Find("img").Each(func(i int, s *goquery.Selection) {
+		s.SetAttr("loading", "lazy")
+	})
+	resHTML, err = doc.Find("body").Html()
+	if err != nil {
+		return commentHTML
+	}
+	return resHTML
+}

backend/app/store/formatter_test.go

@@ -1,6 +1,7 @@
 package store
 
 import (
+	"strconv"
 	"testing"
 	"time"
 
@@ -24,6 +25,11 @@ func TestFormatter_FormatText(t *testing.T) {
 			"<p><a href=\"http://127.0.0.1/some-long-link/12345/678901234567890\">http://127.0.0." +
 				"1/some-long-link/12345/6789012...</a></p>\n!converted", "links",
 		},
+		{
+			"something <img src=\"some.png\"/>  _aaa_",
+			"<p>something <img src=\"some.png\" loading=\"lazy\"/>  <em>aaa</em></p>\n!converted",
+			"lazy image",
+		},
 		{"&mdash; not translated #354", "<p>— not translated #354</p>\n!converted", "mdash"},
 		{"smth\n```go\nfunc main(aa string) int {return 0}\n```", `<p>smth</p>
 <pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">(</span><span class="nx">aa</span> <span class="kt">string</span><span class="p">)</span> <span class="kt">int</span> <span class="p">{</span><span class="k">return</span> <span class="mi">0</span><span class="p">}</span>
@@ -114,3 +120,24 @@ func TestFormatter_ShortenAutoLinks(t *testing.T) {
 		assert.Equalf(t, tt.out, got, "check #%d", n)
 	}
 }
+
+func TestCommentFormatter_lazyImage(t *testing.T) {
+
+	tbl := []struct {
+		inp, out string
+	}{
+		{"", ""},
+		{`blah <img src="some.png" />`, `blah <img src="some.png" loading="lazy"/>`},
+		{`blah <img src="some.png" loading="lazy"/>`, `blah <img src="some.png" loading="lazy"/>`},
+		{`blah <img src="some.png"/> ххх <img src=http://example.com/pp2.jpg>`, `blah <img src="some.png" loading="lazy"/> ххх <img src="http://example.com/pp2.jpg" loading="lazy"/>`},
+	}
+
+	f := NewCommentFormatter(nil)
+	for i, tt := range tbl {
+		tt := tt
+		t.Run(strconv.Itoa(i), func(t *testing.T) {
+			assert.Equal(t, tt.out, f.lazyImage(tt.inp))
+		})
+	}
+
+}